[drivewizard]

Mr. Antley. I don't know whose screws you work on but Trane screws will not get hurt by a little liquid. I've seen the new 134a aircooled screws run sweating from the suction valve to the discharge valve. That was with 45 deg LWT, and a 55 deg day. Granted its not designed to run that way forever, but this one ran this way for about 45 minutes, before problem was fixed.
Also It's probably not a good idea to charge liquid into the discharge service valve. Could end up on top of the valves, pistons, screws, etc.
But, I do agree with most of your posts.

 

[caosesvida]

I believe the the reccomended pressure difference for using the guage and a metering device is 10 psi, although I think I go a little higer than that at times. (between tank pressure and system pressure)

 

[-80guru]

Come on guys you can charge with vapor, you just need to keep the bottle in a bucket of hot water, (not over 120F)
)lol. I can see poor paytonhvac having to carry a bucket of hot water onto one of those roofs he showed us in Arizona. Paytonhvac thinking," gotta get this bucket of hot water so I can be sure to charge only with vaPOOORAAAHHH. Disclaimer, "not picking on paytonhvac". It,s just some of the things I 've seen paytonhvac show us makes me want to get out of the trade, and I don't experience a tenth of what he does.

 

[valdelocc]

I' charge small units in the low side,vapor only I' use a heat gun to raise the temp of the freon,For bigger system when possible I back seat the discharge and let the comp suck it into the reseiver,I'm kind of old fashion cause after all I' get pay by the hour

 

[beenthere]

Those that don't charge by liquid now, might want to start practicing, for r410a.

 

[william antley]

Mr. Antley. I don't know whose screws you work on but Trane screws will not get hurt by a little liquid. I've seen the new 134a aircooled screws run sweating from the suction valve to the discharge valve. That was with 45 deg LWT, and a 55 deg day. Granted its not designed to run that way forever, but this one ran this way for about 45 minutes, before problem was fixed.
Also It's probably not a good idea to charge liquid into the discharge service valve. Could end up on top of the valves, pistons, screws, etc.
But, I do agree with most of your posts.

drivewizard, at the time I was relatively new to working on large chillers and this one was a TRANE R-Series chiller with two 250 ton screws and using R-22 in the system, my first with screw compressors. My boss made me very well acquainted with his reasoning for NEVER getting liquid into a screw due to the close tolerances of the rotors. I can't remember right offhand but, I believe the clearance is only a few thousandths of an inch, some of that for oil, I'd have to get out one of my compressor manuals to know how much exactly. Those close tolerances are why I don't like to let any liquid into a screw, I can't afford to replace them.
As for liquid into a recip, I try very hard not to do this as UNDER NO CIRCUMSTANCES can a liquid be compressed. A rod will break, a piston will be punctured or the crankshaft may get thrown. I have, and still do, meter through my gauges with a 10 psig or less differential pressure between what I'm putting into the system and the actual suction pressure.
I still use my Imperial Quik-Charge and have experienced no difficulties, other than it doesn't charge as fast as I'd like it to at times but, I still use it.
There are as many different techniques to "Quick Charge" a system as there may be techs doing this type of work. We have our favorite methods and will use them.
Charging into the discharge port of a compressor should not ever cause any problems with the valves, pistons, etc. since that liquid is going to move into and past the condenser coil. It can't get back into the cylinder of a recip as the valve plate doesn't move in that direction. If there is an amount of liquid on top of the valve plate, it will get pushed off and into the condenser from the compression cycle, no harm done. Scrolls would behave in a similar fashion.
Also, some units do not have a liquid pressure port, only a discharge pressure port as well as the suction pressure port. Can't refill it any other way except to install a Schrader in the liquid line somewhere. Doing that may be more trouble than it is worth in some instances.
I hope this gives you some better insight as to why I do as I do. If not, drop me a line and we can discuss it some more.

 

[timjimbob]

I have come across old systems in which the old system has a stuck low side service valve that will not open. Some Carriers also don't have suction port. I charge liquid through the liquid high side and valve it as if I am pumping down the system. This draws refrigerant into the system. Check system pressures (at least hi side)every once in a while, otherwise you won't now if you charged enough.

I install a quarter inch MPT to FPT sight glass on my gauges to allow me to see and throttle liquid.

 

[beenthere]

So how do you know if the charge is right with only 1 guage hooked up.

 

[timjimbob]

you don't. Old systems, who cares.
Charge by subcooling.

 

[beenthere]

The customer that can't afford to replace the unit.

To each his own.